The present invention relates to a motorcycle tire suitable for off-road traveling, and more particularly to an off-road motorcycle tire having a steering stability improved by devising the circumferential profile shape of the surface of blocks provided in the tread surface.
Tires for traveling on unpaved roads or rough terrain, e.g., off-road racing motorcycle tires, are provided with a block type tread pattern in which a plurality of blocks defined by tread grooves are formed in a tread portion, in order to secure a good traction performance on rough terrain, as disclosed for example in JP-A-11-078427.
In general, as shown in FIGS. 7A and 7B, a tread portion “a” of these tires has a single circular arc tread profile Pa having a tire shaft center “i” as the center of arc in a circumferential section parallel to the tire equatorial plane Cc. Ground-contacting top surface “bs” of each of blocks “b” which constitute a block pattern is formed into a convex arc profile shape along the tread profile Pa in the circumferential section. The radius “ra” of curvature of the tread profile Pa in the circumferential section at the equatorial plane Cc is identical with half of the outer diameter D of the tire (ra=D/2). In the meridional cross section perpendicular to the tire equatorial plane Cc, the tread portion “a” has a smooth convex arc profile Pb connecting both tread edges Te, Te. The top surface “bs” of each of the blocks “b” is formed into a convex arc profile shape along the tread profile Pb in the meridional cross section.
However, the blocks “b” having a top surface “bs” of such a profile shape have a problem that the ground contact pressure at the periphery of the block top surface “bs” becomes low as compared with a central portion of the block top surface “bs”, so the edge effect brought by block edges is not effectively exhibited and no satisfactory traction performance is obtained.
Accordingly, it is an object of the present invention to provide an off-road motorcycle tire having an improved traction performance.
This and other objects of the present invention will become apparent from the description hereinafter.